The present invention relates to a face plate sander, especially a belt sanding machine, e.g. comprising two sanding units and, as seen in the feed direction, in front of, between and behind these units guides or pressure beams for setting the sanding depth. The inventive device comprises a table for pressing a workpiece against the sanding units and the guides, the table being designed, according to the invention, in such a manner as to allow both dimensioning or adjusting of the workpiece to an almost exact plane-parallel shape and finish sanding of the workpiece with a very accurate, predetermined sanding depth no matter whether the workpiece has a thickness which varies considerably in the feed direction or in a direction transverse thereto.
Conventional sanding machines of the type indicated above usually comprises a feeding conveyor provided below the sanding units for feeding the workpieces through the machine. The table such as mentioned above is provided below the feeding conveyor and has the purpose of pressing the workpiece supported by the conveyor with a suitable force against the sanding units and the guides. In conventional sanding machines the table proper is usually completely rigid. However, the table is resiliently suspended to allow minor deviations from the intended dimensions of the workpieces. Even if the table is resilient in a way, this does not mean that the sanding depth is completely independent of the thickness distribution of the workpiece. Thus, conventional sanding machines usually have a bigger working depth at such portions of the workpiece having a bigger thickness, as the pressing force of a rigid table, due to the spring suspension, will increase with the thickness of the workpiece. The reason for this is that the spring means provide a pressing force against the sanding units that is proportional to the extent of deformation of the spring means.
Further, the rigid table of a conventional sanding machine has the drawback that the workpiece could be exposed to very large local loads if there is a locally protruding portion facing the feeding conveyor. In such a case the total spring force of the table will be concentrated on this small portion which might cause deformations of the workpiece, in turn causing a much increased sanding depth at a point opposite the protruding portion. In such cases it often happens that the sanding depth of a conventional sanding machine will be of such a magnitude that the veneer of a veneered workpiece is completely sanded through.
The present invention has for its object to provide a sanding machine of the kind indicated above and designed to eliminate the above problems and difficulties in achieving an accurately defined sanding depth irrespectively of irregularities of the thickness of the workpiece. Thus, the invention has for its object to provide a device for defining the sanding depth so accurately that there is no risk of sanding through even a thin layer of varnish on the workpiece.